1. Field of the Invention
The present invention relates to a color image display method and apparatus, and particularly to a technique for performing a color display which does not rely on a display device.
2. Description of Related Art
As described in Japanese Laid-open Patent Application NO. Hei-4-291591, according to this type color image display apparatus, RGB image data are subjected to inverse gamma correction, matrix calculation and then gamma correction to display an image.
A conventional color image display apparatus will be described with reference to FIG. 8. The conventional color image display comprises an inverse gamma correction circuit 101, a color transformation matrix calculator 102, a gamma correction circuit 103 and a display device 104 such as a CRT (Cathode Ray Tube).
An input RGB signal is subjected to inverse gamma correction in the inverse gamma correction circuit 101 so that the gamma characteristic of a specific TV camera is in inverse form. This correction operation serves to return the TV camera signal to a linear RGB signal.
The linear RGB signal thus obtained is subjected to the matrix calculation in the color transformation matrix calculator 102 whose coefficient is variable. The color transformation matrix is a matrix for correcting the difference between RGB fluorescent materials (fluorescent substances) at input and output sides and the difference between white colors at the input and output sides. The RGB signal thus matrix-calculated is subjected to the gamma correction which is matched with the display device 104 such as a CRT in the gamma correction circuit 103, thereby displaying an image.
However, this type of conventional color image display apparatus as described above is not provided with any means for obtaining the coefficient of the color transformation matrix calculator 102 and the characteristics of the inverse gamma correction circuit 101 and the gamma correction circuit 103 from the external side. Therefore, it is necessary to beforehand assume the color characteristic of an image to be displayed and input it into the display apparatus.
Japanese Laid-open Patent Application No. Hei-4-291591 discloses a color display apparatus which can solely perform color reproduction having no color reproduction error on image signals having plural different color reproduction characteristics in accordance with each of various systems. In this color display apparatus, it is proposed that the matrix coefficient is controlled to be variable in the color transformation matrix calculator 102, however, there is not any means for obtaining the matrix coefficient itself.
Therefore, in the color display apparatus as described above, the color correction can be accurately performed by only a specific display device, and no accurate color correction can be performed by using other display devices.
Further, according to this type of conventional color image display apparatus, the three correction processing steps of the inverse gamma correction, the matrix correction and the gamma correction are carried out at all times. In this case, actually, there may be a case where it is sufficient to perform only the gamma correction. However, an extra processing time is needed because the inverse gamma calculation and the matrix correction which are not required are also carried out.
In addition, in this type of conventional color image display apparatus, the color correction based on the matrix calculation is performed, and thus accurate color correction which is based on more complicated non-linear transformation processing cannot be performed.